Filtering antenna is designed based on Chebyshev response which has a ripple on its S21, but the gain response in filtering antenna does not perform a ripple. How can that be?
It depends on the amount of ripple you designed for. Sometimes the ripple gets smoothed out by losses or by tuning.
I am often constrained to do Chebyshev impedance matching of our antennas and I never pass on the opportunity to complain about it. Butterworth matching, sure ... but not Chebyshev matching.
Chebyshev matching depends on a pure, resistive termination on both the source and the load. This is never the case with any antenna I've ever designed. As soon as the load departs from pure resistance, the criterion for a Chebysev impedance match vanish. Butterworth matching, however, is far more robust aganst load variations.
If you connect an isolator (a remarkable piece of work) in series with the antenna you remove the impedance variations and you will get your Chebyshev response. This is seldom done because isolators and circulators are usually more costly than the antenna alone.
Dear Mam,
This happens because you chose wide frequency steps when calculating the gain value as a function of frequency. The simulation programs use linear interpolation between every two adjacent frequency steps, so the resulted curve appears to be flat. Please, decrease the frequency step size (increase the number of frequency samples) and you are going to see a difference.
Hearing from you.
Good Luck
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